Integration of electronics with lithium niobate photonics

ABSTRACT

An electro-optical modulator assembly including a transistor including a gate, a drain, and a source disposed on a substrate, a photonic modulator including a first waveguide structure positioned between a first electrode and a second electrode, the photonic modulator being integrated with the transistor on the substrate, and a metal connection coupled between the drain of the transistor and one of the first and second electrodes of the photonic modulator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 120 as a continuationof U.S. Pat. Ser. No. 17/731,369, titled “INTEGRATION OF ELECTRONICSWITH LITHIUM NIOBATE PHOTONICS,” filed Apr. 28, 2022, now U.S. Pat. No.11/747,704, which claims priority under 35 U.S.C. § 121 as a division ofU.S. patent application Ser. No. 16/859,454, titled “INTEGRATION OFELECTRONICS WITH LITHIUM NIOBATE PHOTONICS,” filed Apr. 27, 2020, nowU.S. Pat. No. 11,340,512, each of which is hereby incorporated herein byreference for all purposes.

BACKGROUND 1. Field of Invention

Embodiments of the invention relate generally to photonic modulators andmore particularly photonic modulators for converting signals carryinginformation in the radio frequency (RF) energy domain to signalscarrying the information in the optical frequency energy domain.

2. Discussion of Related Art

As is known in the art, photonic, or electro-optic, modulators have beenused to convert radio frequency (RF) energy to optical energy. Sometypes of photonic modulators include a waveguide structure disposedbetween cladding layers used to confine optical energy (e.g., from alaser) introduced into one end of the waveguide structure and thenpassing through the waveguide structure to a detector. One type ofwaveguide structure includes Lithium Niobate waveguide material which isamong the most promising material for modulator devices. Due toever-increasing performance requirements, at higher modulationfrequencies (e.g., 100 GHz and above) there has been a demand tominiaturize or shorten modulators and associated electronic drivingcircuits to enable wider frequency bandwidth and lower RF parasiticeffects, where the latter can degrade performance of the modulator.

SUMMARY

One aspect of the present disclosure is directed to an electro-opticalmodulator assembly including a transistor including a gate, a drain, anda source disposed on a substrate, a photonic modulator including a firstwaveguide structure positioned between a first electrode and a secondelectrode, the photonic modulator being integrated with the transistoron the substrate, and a metal connection coupled between the drain ofthe transistor and one of the first and second electrodes of thephotonic modulator.

In one embodiment, a first oxide layer disposed on a top side of thetransistor is bonded to a second oxide layer disposed on a bottom sideof the photonic modulator. In some embodiments, the transistor isarranged in proximity to the photonic modulator to minimize a length ofthe metal connection and enable operation of the photonic modulator atfrequencies above 100 GHz. In certain embodiments, the transistor is aIII-Nitride transistor. In one embodiment, the transistor is a GalliumNitride (GaN) High-Electron-Mobility Transistor (HEMT).

In some embodiments, the substrate is one of a Silicon (Si) substrateand a Silicon Carbide (SiC) substrate. In certain embodiments, thephotonic modulator is configured as a Mach-Zehnder interferometer (MZI)modulator and includes a second waveguide structure positioned outsidethe first and second electrodes. In one embodiment, the first and secondwaveguide structures are fabricated from at least one of Lithium Niobate(LiNbO₃) and Silicon Nitride (SiN) and configured to propagate anoptical energy signal.

In various embodiments, the transistor is configured to receive aradio-frequency signal at the gate and to provide a modulation voltageto one of the first and second electrodes via the metal connection toinduce a phase shift in the optical energy signal of the first waveguidestructure. In some embodiments, the optical energy signal of the firstwaveguide structure is combined with the optical energy signal of thesecond waveguide structure to provide an optical signal having anamplitude modulation corresponding to the radio-frequency signalreceived at the gate of the transistor.

Another aspect of the present invention is directed to a method ofmanufacturing an electro-optical modulator assembly. The method includesproviding a transistor including a gate, a drain, and a source disposedon a first substrate, providing a photonic modulator including a firstwaveguide structure positioned between a first electrode and a secondelectrode, the photonic modulator being disposed on a second substrate,depositing a first oxide layer over the gate, the drain, and the sourceof the transistor, and bonding the first oxide layer of the transistorto a second oxide layer of the photonic modulator such that the photonicmodulator is integrated with the transistor on the first substrate.

In one embodiment, bonding the first oxide layer of the transistor tothe second oxide layer of the photonic modulator incudes removing thesecond substrate to expose the second oxide layer of the photonicmodulator. In some embodiments, the second substrate is removed usingplasma processing and/or a back-grinding process. In certainembodiments, bonding the first oxide layer of the transistor to thesecond oxide layer of the photonic modulator incudes depositing thesecond oxide layer on a bottom side of the second substrate.

In some embodiments, the method includes removing a portion of the firstoxide layer to expose the gate, the drain, and the source of thetransistor, and providing a metal connection between the transistor andthe photonic modulator to couple the drain of the transistor to one ofthe first and second electrodes of the photonic modulator. In certainembodiments, the portion of the first oxide layer is removed using alithography process and/or an etching process. In various embodiments,the metal connection is provided between the transistor and the photonicmodulator using a lithography process and/or a metal lift-off process.

In one embodiment, the transistor is a III-Nitride transistor. In someembodiments, the transistor is a Gallium Nitride (GaN)High-Electron-Mobility Transistor (HEMT). In certain embodiments, thefirst substrate is one of a Silicon (Si) substrate and a Silicon Carbide(SiC) substrate. In various embodiments, the photonic modulator isconfigured as a Mach-Zehnder interferometer (MZI) modulator and includesa second waveguide structure positioned outside the first and secondelectrodes. In some embodiments, the first and second waveguidestructures are fabricated from at least one of Lithium Niobate (LiNbO₃)and Silicon Nitride (SiN) and configured to propagate optical energy.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of at least one embodiment are discussed below withreference to the accompanying figures, which are not intended to bedrawn to scale. The figures are included to provide illustration and afurther understanding of the various aspects and embodiments, and areincorporated in and constitute a part of this specification, but are notintended as a definition of the limits of the invention. In the figures,each identical or nearly identical component that is illustrated invarious figures is represented by a like numeral. For purposes ofclarity, not every component may be labeled in every figure. In thefigures:

FIG. 1A is a diagram illustrating a top-down view of a photonicmodulator;

FIG. 1B is a diagram illustrating a cross-sectional view of a photonicmodulator;

FIG. 1C is a diagram illustrating a cross-sectional view of a photonicmodulator;

FIG. 2 is a diagram illustrating a cross-sectional view of a III-Nitrideelectronic device;

FIG. 3 is a diagram illustrating an electro-optical modulatorarrangement according to one embodiment;

FIG. 4 is a flow chart illustrating a method for manufacturing anelectro-optical modulator assembly according to one embodiment;

FIG. 5A is a diagram illustrating a cross-sectional view of aIII-Nitride electronic device according to one embodiment;

FIG. 5B is a diagram illustrating a cross-sectional view of a photonicmodulator according to one embodiment;

FIG. 5C is a diagram illustrating a cross-sectional view of aIII-Nitride electronic device integrated with a photonic modulatoraccording to one embodiment;

FIG. 5D is a diagram illustrating a cross-sectional view of aIII-Nitride electronic device integrated with a photonic modulatoraccording to one embodiment; and

FIG. 5E is a diagram illustrating a cross-sectional view of anelectro-optical modulator assembly according to one embodiment.

DETAILED DESCRIPTION

It is to be appreciated that embodiments of the methods and apparatusesdiscussed herein are not limited in application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the accompanying drawings. Themethods and apparatuses are capable of implementation in otherembodiments and of being practiced or of being carried out in variousways. Examples of specific implementations are provided herein forillustrative purposes only and are not intended to be limiting. Also,the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use herein of“including,” “comprising,” “having,” “containing,” “involving,” andvariations thereof is meant to encompass the items listed thereafter andequivalents thereof as well as additional items. References to “or” maybe construed as inclusive so that any terms described using “or” mayindicate any of a single, more than one, and all of the described terms.Any references to front and back, left and right, top and bottom, upperand lower, and vertical and horizontal are intended for convenience ofdescription, not to limit the present systems and methods or theircomponents to any one positional or spatial orientation.

As discussed above, photonic modulators can be used to convert RF energysignals into optical energy signals. In some cases, photonic modulatorsmay utilize waveguide structures including different photonic materialsintegrated with Lithium Niobate (LiNbO₃) to provide improvedperformance. For example, FIG. 1A illustrates a diagram of aMach-Zehnder interferometer (MZI) modulator 100. The modulator 100includes an input 102, an output 104, a waveguide structure 106 a, 106 b(referred to collectively herein as waveguide structure 106), a firstelectrode 108 a, and a second electrode 108 b. In one example, thewaveguide structure 106 may include a first arm 106 a and a second arm106 b. An optical energy signal (e.g., from a laser) may be provided tothe input 102 and split between the two arms 106 a, 106 b. The arms 106a, 106 b may allow the optical energy signal to propagate from the input102 to the output 104. A modulation voltage may be applied to the firstelectrode 108 a and/or the second electrode 108 b to induce a phaseshift in the optical energy signal of the second arm 106 b (i.e., themodulating arm). In some examples, a modulation voltage may also beapplied to third and fourth electrodes (not shown) to induce a phaseshift in the optical energy signal of the first arm 106 a. In someexamples, the modulation voltage applied to the electrode(s) maycorrespond to information carried by an RF energy signal. The opticalenergy signals of the first and second arms 106 a, 106 b mayconstructively and/or de-constructively combine to produce outputoptical energy having an amplitude modulation corresponding to theinformation carried by the RF energy signal.

FIG. 1B illustrates a cross sectional view of a modulation section 120of an MZI modulator. In one example, the modulation section 120 maycorrespond to the electrodes 108 a, 108 b, and the waveguide structureof the second arm 106 b of the modulator 100 of FIG. 1A. As shown, thewaveguide structure of the second arm 106 b may be defined by directlypatterning a slab of Lithium Niobate (LiNbO₃) material 122. Thewaveguide structure of the second arm 106 b is surrounded by SiliconDioxide (SiO₂) cladding layers 124 a, 124 b. The electrodes 108 a, 108 bmay be fixed to the slab of LiNbO₃ material 122 and partially covered bythe SiO₂ cladding layer 124 a. In some examples, the waveguide structureof the second arm 106 b, the slab of LiNbO₃ material 122, the electrodes108 a, 108 b, and the cladding layers 124 a, 124 b may be disposed on aSilicon (Si) substrate 126. While not shown, the waveguide structure ofthe first arm 106 a of the modulator 100 may be configured similar tothe waveguide structure of the second arm 106 b. For example, thewaveguide structure of the first arm 106 a may be defined by directlypatterning a slab of LiNbO₃ material 122, surrounding the patterned slabof LiNbO₃ material 122 by SiO₂ cladding layers 124 a, 124 b, anddisposing the structure on a Si substrate 126, optionally the same Sisubstrate 126 used in the waveguide structure of the second arm 106 b.

In some examples, the waveguide structures 106 a, 106 b may beconfigured differently. For example, FIG. 1C illustrates a crosssectional view of a modulation section 140 of an MZI modulator (e.g.,modulator 100). In one example, the modulation section 140 may besubstantially the same as the modulation section 120 of FIG. 1B, exceptthe waveguide structure of the second arm 106 b is configureddifferently. As shown, the waveguide structure of the second arm 106 bis defined by patterning a Silicon Nitride (SiN) film on the slab ofLiNbO₃ material 122. Likewise, the waveguide structure of the first arm106 a may be configured similarly.

As discussed above, when operating photonic modulators such as themodulator 100 at high frequencies (e.g., above 100 GHz), RF parasiticeffects (e.g., signal reflection, propagation loss, electromagneticinterference, etc.) can degrade performance. In some implementations,such modulators can be designed with a miniaturized form (e.g., relativeto wavelength) to suppress RF parasitic effects within the modulator.However, reducing the size of the modulator can increase the modulationvoltage required to achieve the desired phase shift (e.g., 180°). Inaddition, the distance between voltage circuitry configured to apply themodulation voltage to the electrode(s) and the modulator may contributeto additional RF loss and/or reflections.

A compact, high-frequency photonic modulator arrangement is providedherein. In at least one embodiment, a photonic modulator is integratedwith a III-Nitride electronic device. More specifically, the photonicmodulator is bonded to the electronic device substrate to reduce RFparasitic effects between the devices and enable high frequencyoperation of the modulator (e.g., above 100 GHz).

As discussed above, photonic modulators used in high frequencyapplications may operate with an increased modulation voltage. As such,voltage circuitry configured to provide the modulation voltage to theelectrode(s) of the modulator may include semiconductor devices capableof providing large voltages without entering a breakdown region at highfrequencies. In one example, the voltage circuitry may include one ormore III-Nitride electronic devices. For example, the voltage circuitrymay include one or more Gallium Nitride (GaN) High-Electron-MobilityTransistors (HEMT) to provide the increased modulation voltage. As knownto those skilled in the art, GaN HEMTs can provide high breakdownvoltages while operating at high frequencies (e.g., above 100 GHz). Insome examples, GaN HEMTs can be utilized to provide low noiseamplification. FIG. 2 illustrates a cross sectional view of an exampleof a GaN HEMT 200. As shown, the GaN HEMT 200 includes a source 202, agate 204, and a drain 206. In one example, an Aluminum Gallium Nitride(AlGaN) barrier layer 208 is included between the source 202, the gate204, and the drain 206. In other examples, the barrier layer 208 can bemade from InAIN, InAlGaN, or ScAIN materials. The source 202 and thedrain 206 are fixed to a GaN channel layer 210 and an Aluminum Nitride(AIN) nucleation (or buffer) layer 212 is disposed between the GaNchannel layer 210 and a substrate 214. In some examples, the substrate214 may be made from Si; however, in other examples the substrate may bemade from a Silicon Carbide (SiC) material.

FIG. 3 illustrates an electro-optical modulator arrangement 300 inaccordance with aspects described herein. In one example, the GaN HEMT200 of FIG. 2 is coupled to the modulator 100 of FIG. 1A. As shown, thedrain 206 of the GaN HEMT 200 is coupled to the electrode 108 a of themodulator 100 via a metal connection 302. The GaN HEMT 200 is configuredto provide a modulation voltage via the drain 206 to the electrode 108 ato modulate the optical energy of the second arm 106 b. In someexamples, the electrode 108 b may be coupled to ground or anothervoltage source. While not shown, the GaN HEMT 200 may be configured tooperate with other circuitry to provide the modulation voltage to theelectrode 108 a. For example, an RF modulation source may be coupled tothe gate 204 and the source 202 may be coupled to ground or anothervoltage source. As such, the RF modulation source may provide an RFsignal to the gate 204 to turn the GaN HEMT 200 on and off, providingthe modulation voltage at the drain 206 corresponding to the RF signal.In some examples, the GaN HEMT 200 may be configured to amplify themodulation voltage provided at the drain 206.

In one example, the distance 304 represents a physical distance betweenthe drain 206 and the electrode 108 a. As such, the electrical length ofthe metal connection 302 may correspond to the distance 304. Asdiscussed above, the distance between the voltage circuitry (i.e., theGaN HEMT 200) and the modulator 100 may contribute to parasitic RF loss.As such, reducing the distance 304 between the drain 206 and theelectrode 108 a may improve performance of the modulator 100. FIG. 4illustrates a method 400 of manufacturing an electro-optical modulatorassembly in accordance with aspects described herein. In one example,the electro-optical modulator assembly corresponds to a photonicmodulator integrated with an electronic device. For example, theelectro-optical modulator assembly may correspond to the electro-opticalmodulator arrangement 300 of FIG. 3 . In some examples, the method 400may allow for the distance 304 between the GaN HEMT 200 and themodulator 100 to be reduced, improving performance of the modulator 100at high frequencies.

In one example, the method 400 includes bonding the modulator 100 to theGaN HEMT 200 using an oxide-oxide bonding process. As such, at block402, the GaN HEMT 200 is prepared for the oxide-oxide bonding process.As shown in FIG. 5A, an SiO₂ layer 502 is deposited over the GaN HEMT200. In some examples, the thickness of the SiO₂ layer 502 maycorrespond to the thickness of certain features of the GaN HEMT 200. Forexample, the SiO₂ layer 502 may be thick enough to cover metal contactscorresponding to the source 202, the gate 204, and the drain 206 of theGaN HEMT 200. In certain examples, a planarization process may beutilized to flatten the top of the SiO₂ layer 502.

Similarly, at block 404, the modulator 100 is prepared for theoxide-oxide bonding process. In one example, the Si substrate 126 of themodulator 100 may be removed to expose the SiO₂ cladding layer 124 b.FIG. 5B illustrates the modulation section 120 of the modulator 100 withthe Si substrate 126 removed. In some examples, the Si substrate 126 maybe removed using plasma processing and/or a back-grinding process.Alternatively, in other examples, a thin SiO₂ layer may be deposited onthe back (i.e., bottom) of the Si substrate 126. In some examples, itmay be preferred to remove the Si substrate 126 to maintain or improveperformance of the modulator 100 at high frequencies (e.g., above 100GHz). While not shown, in other examples, the modulator 100 may beconfigured with the modulation section 140 of FIG. 1C and may bemodified in a similar manner.

At block 406, the modulator 100 is integrated onto the substrate 214 ofthe GaN HEMT 200. As shown in FIG. 5C, the SiO₂ cladding layer 124 b ofthe modulator 100 is bonded to the SiO₂ layer 502 of the GaN HEMT 200using an oxide-oxide bonding process to produce an integrated device510. In one example, the area (e.g., layers) above the GaN HEMT 200 maybe removed to provide access to the source 202, the gate 204, and thedrain 206. For example, as shown in FIG. 5D, portions of the layers 122,124 a, 124 b, and 502 above the source 202, the gate 204, and the drain206 may be removed from the integrated device 510 using a lithographyand/or etching process. In other examples, the portion of the SiO₂ layer502 covering the source 202, gate 204, and drain 208 of the GaN HEMT 200may be removed prior to the oxide-oxide bonding process (e.g., prior toblock 406) such that the source 202, gate 204, and drain 208 of the GaNHEMT 200 remain exposed post-bond.

At block 408, a metallization process is applied to the integrateddevice 510. As shown in FIG. 5E, the metallization process may beutilized to produce a metal connection 522 between the GaN HEMT 200 andthe modulator 100 to provide an electro-optical modulator assembly 520.In one example, the metal connection 522 may correspond to the metalconnection 302 of FIG. 3 . The metal connection 522 may couple the drain206 of the GaN HEMT 200 to the electrode 108 a of the modulator 100. Insome examples, the metallization process may include a lithographyand/or a metal lift-off process to connect the drain 206 to theelectrode 108 a. While not shown, in other examples, a similar processmay be utilized to couple the electrode 108 b to ground or a differentvoltage source.

In some examples, by bonding the modulator 100 to the substrate 214 ofGaN HEMT 200, the modulator 100 can be arranged in close proximity(e.g., microns) to the GaN HEMT 200. Being that the modulator 100 andthe GaN HEMT 200 are in close proximity, the length of the metalconnection 522 may be relatively short and the distance between thedrain 206 of the GaN HEMT 200 and the electrode 108 a (e.g., thedistance 304) may be reduced significantly. As such, RF parasiticeffects associated with the electrical connection between the modulator100 and the GaN HEMT 200 can be reduced, and the modulator 100 may beenabled to operate at even higher frequencies (e.g., THz range).

It should be appreciated that embodiments described herein are notlimited to a particular type of III-Nitride electronic device. Asdescribed above, a GaN HEMT can be integrated with a photonic modulatorto provide improved high frequency performance; however, in otherexamples, different III-Nitride materials and/or devices may beutilized. For example, depending on the implementation, the method 400may be adapted to integrate an Indium Nitride (InN) HEMT with thephotonic modulator (e.g., depositing SiO₂ on top of the InN HEMT forbonding). In alternative embodiments, devices other than III-Nitridedevices, such as GaAs, InP, SiC, and Si based devices, may be integratedwith photonic modulators depending on the performance requirements forspecific applications. In addition, in some examples, the method 400 maybe carried out using individual devices (i.e., chips); however, in otherexamples, the method 400 may be carried out at the wafer-level.

Likewise, it should be appreciated that embodiments described herein arenot limited to a specific type of photonic modulator. While the use ofan MZI modulator is described above, in other examples, III-Nitrideelectronic devices can be integrated with different types of modulators(e.g., a resonator modulator).

Accordingly, various aspects and examples described herein provide acompact, high-frequency photonic modulator arrangement. In at least oneembodiment, a photonic modulator is integrated with an III-Nitrideelectronic device. More specifically, the photonic modulator is bondedto the electronic device substrate to reduce RF parasitic effectsbetween the devices and enable high frequency operation of the modulator(e.g., above 100 GHz).

Having described above several aspects of at least one example, it is tobe appreciated various alterations, modifications, and improvements willreadily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be part of thisdisclosure and are intended to be within the scope of the invention.Accordingly, the foregoing description and drawings are by way ofexample only, and the scope of the invention should be determined fromproper construction of the appended claims, and their equivalents.

What is claimed is:
 1. An electro-optical modulator assembly comprising:a transistor including a gate, a drain, a source, and a film forming achannel layer for the transistor disposed on a substrate; a photonicmodulator including a first waveguide structure positioned between afirst electrode and a second electrode, the photonic modulator beingdisposed on the film forming the channel layer for the transistor; and ametal connection coupled between the drain of the transistor and one ofthe first and second electrodes of the photonic modulator.
 2. Theelectro-optical modulator assembly of claim 1, wherein a first oxidelayer disposed on a top side of the transistor is bonded to a secondoxide layer disposed on one side of the photonic modulator.
 3. Theelectro-optical modulator assembly of claim 1, wherein the transistor isarranged in proximity to the photonic modulator to minimize a length ofthe metal connection and enable operation of the photonic modulator atfrequencies up to and above 100 GHz.
 4. The electro-optical modulatorassembly of claim 1, wherein the transistor is a III-Nitride transistor.5. The electro-optical modulator assembly of claim 4, wherein thetransistor is a III-Nitride High-Electron-Mobility Transistor (HEMT). 6.The electro-optical modulator assembly of claim 1, wherein the substrateis one of a Silicon (Si) substrate and a Silicon Carbide (SiC)substrate.
 7. The electro-optical modulator assembly of claim 1, whereinthe photonic modulator is configured as a Mach-Zehnder interferometer(MZI) modulator and includes a second waveguide structure positionedoutside the first and second electrodes.
 8. The electro-opticalmodulator assembly of claim 7, wherein the first and second waveguidestructures are fabricated from at least one of Lithium Niobate (LiNbO₃)and Silicon Nitride (SiN) and configured to propagate an optical energysignal.
 9. The electro-optical modulator assembly of claim 8, whereinthe transistor is configured to receive a radio-frequency signal at thegate and to provide a modulation voltage to one of the first and secondelectrodes via the metal connection to induce a phase shift in theoptical energy signal of the first waveguide structure.
 10. Theelectro-optical modulator assembly of claim 9, wherein the opticalenergy signal of the first waveguide structure is combined with theoptical energy signal of the second waveguide structure to provide anoptical signal having an amplitude modulation corresponding to theradio-frequency signal received at the gate of the transistor.
 11. Theelectro-optical modulator assembly of claim 7, wherein at least one ofthe first and second waveguide structures are fabricated from a SiN filmdisposed on a slab of LiNbO₃.
 12. A method of manufacturing anelectro-optical modulator assembly, the method comprising: forming atransistor including a gate, a drain, and a source disposed on a firstsubstrate; forming a photonic modulator including a first waveguidestructure positioned between a first electrode and a second electrode,the photonic modulator being disposed on a second substrate; depositingan oxide layer over the gate, the drain, and the source of thetransistor; and bonding the oxide layer of the transistor to thephotonic modulator such that the photonic modulator is integrated withthe transistor and the photonic modulator is disposed over a filmforming a channel layer for the transistor.
 13. The method of claim 12,further comprising forming a metal connection between the transistor andthe photonic modulator to couple the drain of the transistor to one ofthe first and second electrodes of the photonic modulator.
 14. Themethod of claim 12, wherein the transistor is a III-Nitride transistor.15. The method of claim 14, wherein the transistor is a Gallium Nitride(GaN) High-Electron-Mobility Transistor (HEMT).
 16. The method of claim12, wherein the first substrate is one of a Silicon (Si) substrate and aSilicon Carbide (SiC) substrate.
 17. The method of claim 12, wherein thephotonic modulator is configured as a Mach-Zehnder interferometer (MZI)modulator and includes a second waveguide structure positioned outsidethe first and second electrodes.
 18. The method of claim 17, wherein thefirst and second waveguide structures are fabricated from at least oneof Lithium Niobate (LiNbO₃) and Silicon Nitride (SiN) and configured topropagate optical energy.